A new orthorhombic boron phase B_51.5–52 obtained by dehydrogenation of “α-tetragonal boron”

Abstract

Abstract

Hydrogenation, dehydrogenation of α-tetragonal boron and its transition to δ-orthorhombic boron

“…This value can be compared with −3.5 eV/(N atom) for B 50 N 2 and −0.5 eV/(C atom) for B 50 C 2 (these values were obtained from [19], though they are not explicitly given there). Hence, the affinity of hydrogen to α-T boron is strong and is in intermediate between C and N. Figure 5 shows the dependence of the cell volume on the H content m. All curves, experiment (green crosses) [20] and DFT calculations (open and filled symbols), nearly have the same slope and show a linear increase of the cell volume by about 10% as the H content increases from m=0 to 12. We do not find an anisotropy in the increase between the a and b lattice directions.…”

“…Ekimov et al [20] studied the effect of annealing on the B 51 H 7.7 samples recovered from the HPHT synthesis. The annealing experiment was performed in an open chamber through which an Ar gas flowed at ambient pressure.…”

“…In the second step, a structure was changed from α-T to δ-O phases. The details of experiment are given in [20].…”

“…Here we are concerned with hydrogenated α-T boron and its relation to a new orthorhombic boron phase. Hydrogenated α-T boron crystals, with compositions B 51.5 H m , were prepared by Ekimov el al [11,20]. Their samples were synthesized by thermal decomposition of decaborane at high temperature (T∼1100°C-1300°C) and high pressure (p=8-9 GPa) and the initial H content was m=7.7.…”

“…However, hydrogen inclusion was later discovered by mass spectroscopy, and two kinds of compositions BH 0.15 and BH 0.09 were found by annealing. Furthermore, the B content varied from 51.5 to 52.0 during the annealing [20]. Whether or not the difference in the B content is due to experimental error is unclear.…”